This invention relates to a power transmission apparatus for a machine, such as a plastic injection molding machine or a press machine, and more particularly to a power transmission apparatus, which includes a coiled torsional spring that serves as a clutch device and that can be wound around a plurality of rollers on a sleeve assembly during rotation of a primary driving gear for transmitting a torque from the primary driving gear to a driven gear.
The object of this invention is to provide a power transmission apparatus, which includes a coiled torsional spring that can be wound around a plurality of rollers on a sleeve assembly during rotation of a primary driving gear for transmitting a torque from the primary driving gear to a driven gear.
According to this invention, a power transmission apparatus includes a sleeve assembly disposed rotatably around a stationary support shaft and having an annular surface unit that is formed with a plurality of axially extending slots therethrough. A primary driving gear is sleeved fixedly on the sleeve assembly, and is adapted to be rotated by a power source. A secondary driving gear is sleeved rotatably on the sleeve assembly. A driven gear is sleeved rotatably on the support shaft. A plurality of rollers are confined respectively and rollably within the slots. A coiled torsional spring is disposed around the sleeve assembly, is spaced apart from the rollers, and is fastened to the secondary driving gear at one end and to the driven gear at the other end. During rotation of the primary driving gear, when the secondary driving gear rotates, the spring is wound around the sleeve assembly so as to clamp and lock the rollers between the spring and the sleeve assembly, thereby transmitting a torque from the primary driving gear to the driven gear. As such, the spring serves as a clutch device.